This application is based on Japanese Patent Application No. 09-166765 filed on Jun. 24, 1997, No. 10-139392 filed on May 21, 1998, No. 10-139393 filed on May 21, 1998, and No. 10-139394 filed on May 21, 1998, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a method of and an apparatus for image processing in which serially fed image data are subjected to digital filtering. The invention is applicable to a digital copying machine or an image-reproducing system which is a combination of a scanner and a printer.
2. Description of the Prior Art
Digital copying machines have heretofore been proposed where image data obtained from the imaging of a document are subjected to xcex3 transform, magnification change, correction of a modulation transfer function (MTF) and formation of a binary image. Correction of the MTF aims at improving picture quality and ordinarily includes two-dimensional digital filtering such as edge sharpening.
With the digital copying machine, the document is scanned in order of successive lines. In concert with the progress of scanning, image data are serially transmitted from each pixel. In order to subject all the image data to two-dimensional digital filtering at a time, image data for preceding lines have to be temporarily stored until image data for the last line is obtained.
In order to effect edge sharpening by means of, e.g., a Laplacian filter which is the size of 5xc3x975, it has been conventional practice in the past to use four line memories for temporarily storing image data for four lines. These image data are taken out of the line memories in concert with the progress of scanning of the fifth line. Image data transmitted by pixels located at the same locations in the five lines are fed to a filter circuit at a time.
Heretofore, as the number of bits per pixel is increased and as the higher resolution is required for reading an image, a stringent necessity for larger capacity has come upon the line memories and has resulted in high costs.
Let it be assumed that image data consist of 8 bits (i.e. 256 scales) per pixel and that a document printed or handwritten on a sheet of paper parallel with the longer sides of the paper which is the size of DIN A4 is read with a resolution of 600 dpi. Then the quantity of data per line amounts to about 8 kilobytes. This means that a storage capacity of 32 kilobytes in total is needed for four lines. Large-capacity memories make it difficult to be mounted on a single substrate together with other data processing circuits.
The primary object of the present invention is to provide an improved method and apparatus for processing image data.
Another object of the present invention is to provide a method and apparatus for processing image data which is capable of reducing a capacity of memory for synchronizing a plurality of lines of image data.
To achieve at least one of the above mentioned objects, the method for processing image data of one aspect of the present invention comprises the steps of (a) synchronizing transfer of a plurality of sets of compressed image data thus parallelly transferring the plurality of compressed image data and (b) executing a predetermined process on the plurality of sets of the compressed image data synchronized in the step (a).
According to another aspect of the present invention, the method for processing image data comprises the steps of (a) compressing image data and (b) executing a predetermined image correction process on the image data compressed in step (a).
Further to the above mentioned methods, an apparatus essentially employing at least one of the above mentioned methods is also within the scope of the present invention.